1. Field of the Invention
The present invention relates to a solid electrolytic capacitor including a conductive polymer compound as a solid electrolyte and a method of manufacturing the solid electrolytic capacitor.
2. Description of the Background Art
In connection with size and weight reductions of electric equipment in recent years, a small capacitor of a large capacity for high frequencies has come to be required. As such a capacitor, a solid electrolytic capacitor using a conductive polymer compound to form a solid electrolyte layer has been proposed.
The solid electrolytic capacitor has a problem of a decrease in adhesion between a dielectric oxide coating, which is an inorganic material layer formed by oxidation of a surface of an anode body formed with a sintered body of a valve metal such as tantalum, niobium, titanium, or aluminum, and a solid electrolyte layer which is an organic material layer (a conductive polymer compound layer) formed on the dielectric oxide coating, which results in an increased leaked current, an increased ESR (Equivalent Series Resistance) and decreased reliability.
Therefore, when the conductive polymer compound layer is formed on the dielectric oxide coating, a partial conductive polymer compound layer covering a portion of the dielectric oxide coating is generally formed beforehand by chemical oxidative polymerization, and then a full-scale conductive polymer compound layer covering a whole surface of the dielectric oxide coating is formed by electrolytic oxidative polymerization. The adhesion between the dielectric oxide coating and the conductive polymer compound layer, however, is insufficient even when the conductive polymer compound layer is formed as such.
To solve the problem, a method for increasing the adhesion between the dielectric oxide coating and the conductive polymer compound layer has been proposed, which includes steps of forming the dielectric oxide coating on the surface of the anode body, treating a surface thereof with a silane coupling agent, and then forming on the surface the conductive polymer compound layer as a solid electrolyte layer to let the silane coupling agent be interposed between the dielectric oxide coating and the conductive polymer compound layer (for example, see Japanese Patent Laying-Open Nos. 02-074021, 04-073924 and 08-293436).
Though the adhesion between the dielectric oxide coating and the conductive polymer compound layer is increased with existence of the silane coupling agent, current collection by the conductive polymer compound layer is inhibited because the silane coupling agent itself is an insulator, and therefore the ESR is increased and a capacitance is decreased.